This application relates to a shut-down and/or annunciator system for an automatic reaction vessel that is used to treat tissue specimens or the like by immersing them in reagents. The specific application in which the system was first used was in a histological tissue processor of the type described in U.S. Pat. No. 4,141,312. In that patent, the vessel is referred to as a tissue container.
In a histological tissue processor of the type described in the above noted patent, tissue specimens are immersed in a reagent by selectably connecting the vessel to a reagent source or reagent container by a conduit that opens into the vessel and into the bottom of the reagent container and by drawing a vacuum upon the vessel. The vacuum within the vessel draws reagent from the reagent container. the specimens are soaked for some period of time in the reagent. Sometimes reagents are heated by heating the vessel and/or a vacuum is drawn over the surface of the reagent during the soak. Therefore, it is absolutely essential that the vessel fills with the reagent when the specimens are positioned therein. Otherwise, the specimens could quickly be destroyed by heat and/or vacuum at great expense and inconvenience. In the reaction vessel of the type described in the noted patent, the reagent is returned to the reagent containers by gravity drain.
Two conditions may result in the failure of the vessel to fill with reagent when the reagent is to be drawn into the vessel by vacuum. Either the vacuum system fails or there is a blockage between the reaction vessel and the reagent source. A valid shut-down and/or annunciator system, of course, must respond to any circumstances under which the vessel does not fill.
It is undesirable to place a float-type sensor in the vessel as float sensors tend to become battered by specimen holders and even clogged by the reagents. (Typically the specimens in a tissue processor are impregnated with paraffin as the last step in preparation for analysis.) A float-type sensor also requires leads passing through the walls of the reaction vessel introducing a potential location for leakage.
It is an advantage according to this invention to provide a shut-down and/or annunciator system that detects the unfilled condition of the reaction vessel without placing a flow-type level sensor within the vessel.
By way of background, it should be understood that when a vacuum is drawn upon a vessel at the beginning of the fill cycle and the vessel is connected to the reagent source, the vacuum will exceed a preselected limit. It will continue to exceed the preselected limit as long as the source can supply reagent. When the source is exhausted of reagent, air is drawn through the reagent source and the vacuum over the vessel will be diminished. Thus, the vacuum will no longer exceed the preselected limit when the air is drawn into the vessel at the end of the normal filling cycle. If the reagent source is plugged or a valve between the vessel and the reagent container does not open, the vacuum will remain above the preselected level at the end of the normal fill cycle. If the vacuum system is defective, the vacuum will never exceed the preselected limit.
The commercial embodiment of the tissue processor described in the noted patent has been sold for over a year prior to the filing of this application. In that embodiment, the vacuum in the reaction vessel is limited by a pressure release valve to less than four inches of mercury during the filling cycle which normally lasts about one minute and twenty-five seconds. The vacuum is limited to about four inches of mercury to minimize the boiling action that takes place when the solvent source becomes empty and air enters the vessel. When the container of solvent is emptied and air enters the reaction vessel through the solvent source container, the drop in vacuum below 1.5 inches of mercury is sensed to switch the vacuum pump off and to close the valve connecting the tissue container to the reagent container.